It is current practice in spinal surgery to use bone fixation devices to improve the mechanical stability of the spinal column and to promote the proper healing of injured, damaged or diseased spinal structures. Typically, corrective surgery entails the removal of damaged or diseased tissue, a decompression of one or more neural elements, followed by the insertion of an intervertebral implant for the purposes of a fusion or disc arthroplasty. In cases where spinal fusion is the desired surgical outcome, the final step is often to apply a bone plate in order to immobilize adjacent vertebral bones to expedite osteogenesis across said vertebral segments.
Most current surgical techniques require that damaged vertebral tissue be placed under rigid axial distraction throughout much of the procedure. This allows for greater ease in the removal of tissue, provides a larger working space for instrument maneuverability, enhances the surgeon's visibility and assists with the fit of the interbody implant once the distractor apparatus is removed. Conventional distraction of the spine typically employs the use of temporary “distractor pins” placed directly into the bone tissue adjacent to the disc space to be repaired, which are subsequently induced to move axially by the attachment and adjustment of a secondary tool. An alternative method employs the use of a ratcheting spreader device which is inserted directly into the vertebral interspace and is adjusted thereafter to achieve desired distraction. These distraction methods offer an imprecise means to restore preferred vertebral alignment, add several steps, require more time to install and remove, increase the risk for entwining of surrounding vascular structures or peripheral nerves and can present significant physical impediments and technical challenges to the surgeon. Additionally, because the distractor device remains temporarily inserted during the decompression and fusion portions of the procedure, the surgeon must essentially work around the obtrusive projecting devices while completing the majority of the surgery.
It is also known that current distraction methods, while generally not designed or intended for this purpose, are often employed to adjust or maintain the angular alignment of adjacent vertebra in an attempt to restore normal lordotic curvature. The outcomes are varied, the degree of distraction and the angular correction produced by current distraction methods are often imprecise, require substantial subjective assessment by the surgeon and can vary significantly from patient to patient. Further, excessive distraction can result in a negative surgical outcome which can result in nerve damage or on-going post surgical pain for the patient.
There is a high degree of dimensional variability in the resulting intervertebral volume after distraction has been achieved using these devices. As a result, the surgeon must often make “trial and error” assessments as to the size and shape of the interbody implant to be inserted and may be required to customize the implant intraoperatively prior to final insertion.
In the conventional method, once the implant has been inserted, the distractor device is removed and the vertebrae can be secured by the attachment of a bone plate. Such bone plates, including a plurality of bone screws, are applied near the completion of the procedure to provide vertebral fixation and prohibit undesirable migration of the intervertebral implant.
Several design constructs have already been proposed in which a device is applied to adjacent vertebrae at the start of a procedure, prior to tissue removal, for the purposes of achieving and maintaining preferred vertebral alignment while serving also to constrain tissue removal throughout the procedure. The disclosed or published art in this method can generally be categorized into two broad categories: removable devices and permanently implantable devices.
The removable devices differ from the present proposed invention in that the devices used to maintain preferred vertebral alignment are temporary inserts and are subsequently removed after tissue removal so that a repair device may be delivered thereafter. The prior art which discloses permanently implantable devices differs in that the devices function solely to maintain preferred vertebral alignment and are not part of a comprehensive system and related method to precisely control and permanently maintain the preferred spatial relationship of adjacent vertebral members for controlled tissue removal and delivery of a repair device.
Removable Devices
U.S. Pat. No. 7,153,304 entitled Instrument System for Preparing a Disc Space Between Adjacent Vertebral Bodies to Receive a Repair Device, issued Dec. 26, 2006 to Robie et al., discloses a removable instrument system for preparing a disc space between adjacent vertebral bodies using a series of distractors that restore natural lordosis before a temporary template is attached for vertebral immobilization and to function as a guide for an insertable reamer meant for tissue removal.
U.S. Pat. No. 7,083,623 to Michelson, entitled Milling Instrumentation and Method for Preparing a Space Between Adjacent Vertebral Bodies, issued Aug. 1, 2006, discloses a removable milling device and method for preparing a space between adjacent vertebral bodies which essentially maintains preferred vertebral alignment while functioning as a saw guide to control bone and soft tissue removal.
US Pat. App. 2005/0043740 to Haid, entitled Technique and Instrumentation for Preparation of Vertebral Members, published Feb. 24, 2005, discloses a removable instrumentation set and technique for preparation of vertebral members utilizing a docking ring which is temporarily applied to the anterior spine to maintain preferred vertebral alignment and to function as a docking plate for an articulating bone removal device.
U.S. Pat. No. 7,033,362 to McGahan, entitled Instruments and Techniques for Disc Space Preparation, issued Apr. 25, 2006, discloses a removable instrumentation set and method for disc space preparation whereby an intervertebral device is temporarily inserted for the purpose of constraining tissue removal and guiding the position of an intervertebral repair device.
US Pat. App. 2003/0236526 to Van Hoeck, entitled Adjustable Surgical Guide and Method of Treating Vertebral Members, published Dec. 25, 2003, discloses a removable surgical guide and method with adjustable functionality for the preparation of adjacent vertebra.
US Pat. App. No. 2006/0247654 to Berry, entitled Instruments and Techniques for Spinal Disc Space Preparation, published Nov. 2, 2006, discloses a removable milling instrument assembly for vertebral endplate preparation which constrains a cutting path obliquely oriented to the axis of the vertebra.
Permanently Implanted Devices
US Pat. App. 2004/0097925 to Boehm, entitled Cervical Spine Stabilizing System and Method, published May 20, 2004, discloses a permanently implantable spine stabilizing system and method whereby a plate configured to be positively centered along the midline is placed to retain adjacent vertebra in a desired spatial relationship during discectomy and fusion procedures. The disclosed invention uses a series of temporary implants and removable drill templates in an attempt to assure the alignment of the implanted device along the midline of the spinal column. This alignment is typically not considered to be significant in determined the clinical outcome of the procedure and is further considered impractical for the purposes of performing repair procedures on multiple adjacent disk spaces due to the normal scoliotic curvature of the spine.
US Pat. App. 2005/0149026 to Butler et al., entitled Static and Dynamic Cervical Plate Constructs, published Jul. 7, 2005, describes an implanted cervical bone plate having a graft window located between the bone screw holes for the purposes of providing visualization and access to an intervertebral implant. The device described is applied after the intervertebral space has been repaired and after the implant has been positioned. The specification states specifically that an appropriately “sized dynamic plate is placed over the inserted bone implant”; thereafter the bone plate is located with respect to the implant by viewing the implant through the graft window and secured in place using bone screws.
Additional bone plate devices are disclosed in U.S. Pat. No. 3,741,205 to Markolf et al, and US Pat. Apps. 2005/0149026 to Butler et al. and 2007/0233107 to Zielinski.
Accordingly, it is apparent that there remains a need for and advantage to a permanently implantable spinal repair system and related method whereby the final preferred vertebral alignment and fixation occurs prior to the surgical removal of damaged tissue, without the use of temporary implants or fasteners and where the surgical procedures can be performed there-through in the minimum amount of time with the minimum number of entries into the surgical field. It is further apparent that there is a need for a system wherein subsequent recovery procedures can be performed with minimal effort should implantation fail or should subsequent surgery be required.